1. Field of the Invention
The present invention pertains to patient interface devices structured to deliver a flow of breathing gas to a user, and, in particular, to a sealing cushion for a patient interface device that has an inverted geometry as compared to traditional cushions wherein a sealing flap portion of the cushion is located on the inside of a support portion of the cushion.
2. Description of the Related Art
There are numerous situations where it is necessary or desirable to deliver a flow of breathing gas non-invasively to the airway of a patient, i.e., without intubating the patient or surgically inserting a tracheal tube into the patient's esophagus. For example, it is known to ventilate a patient using a technique known as non-invasive ventilation. It is also known to deliver positive airway pressure (PAP) therapy to treat certain medical disorders, the most notable of which is OSA. Known PAP therapies include continuous positive airway pressure (CPAP), wherein a constant positive pressure is provided to the airway of the patient in order to splint open the patient's airway, and variable airway pressure, wherein the pressure provided to the airway of the patient is varied with the patient's respiratory cycle. Such therapies are typically provided to the patient at night while the patient is sleeping.
Non-invasive ventilation and pressure support therapies as just described involve the placement of a patient interface device including a mask component having a soft, flexible sealing cushion on the face of a patient. The mask component may be, without limitation, a nasal mask that covers the patient's nose, a nasal/oral mask that covers the patient's nose and mouth, or a full face mask that covers the patient's face. Such patient interface devices may also employ other patient contacting components, such as forehead supports, cheek pads and chin pads. This interface should be comfortable and maintain a robust seal while at the same time not creating air-path restrictions and/or increased difficulty in breathing. In addition, the sealing cushion should be comfortable enough to ensure patient compliance, but must also be stable and consistently provide a seal for compliance. The patient interface device is connected to a gas delivery tube or conduit and interfaces the ventilator or pressure support device with the airway of the patient, so that a flow of breathing gas can be delivered from the pressure/flow generating device to the airway of the patient. It is known to maintain such devices on the face of a wearer by a headgear having one or more straps adapted to fit over/around the patient's head.
One known mask geometry that is commonly used is shown in FIG. 1A. As seen in FIG. 1A, that mask geometry employs a cushion assembly 2 that includes a cushion member 4 coupled to a support ring 6 (which facilitates connection of cushion assembly 2 to a rigid or semi-rigid faceplate or shell). Cushion member 4 includes a bottom portion 8 coupled to support ring 6, wherein bottom portion 8 also includes an outer wall 10. In addition, cushion member 4 also includes a support portion 12 structured to provide a support function for cushion assembly 2, and a sealing flap 14, structured to provide a suitable seal against the user's face during use.
As seen in FIG. 1A, sealing flap 14 and support portion 12 are integrated as two features within the same component, and support portion 12 is located on the inside of sealing flap 14. In other words, sealing flap 14 is located above and outside the inner support portion 12. In this configuration, sealing flap 14 must be made long enough (L1 in FIG. 1A) to cover support portion 12, and thus sealing flap 14 requires an additional length L2 as compared to support portion 12 to ensure that it extends out over support portion 12. This extra flap length increases part height, results in unnecessary additional length in the sealing flap, and often times undesirably encroaches over the user's nares at the nostril area cushion assembly 4 during use. The extra flap length also often causes undesirable bunching of sealing flap 14 while in engagement with the user's face, which may cause leak paths, visual obstruction to the user, and general annoyance and comfort issues. As used herein, bunching shall refer to an area where, when the cushion is donned by the user, extra sealing flap length collects and folds/curls over itself, resulting in bunches or folds of sealing flap (as shown in FIG. 1B). These areas of bunching also result in zones which are at risk to compliance issues (wherein compliance is expressed as ΔV/ΔP (the change in volume divided by the change in pressure). Cushion assembly 2 also requires a curved, cantilever style support portion 12 inside sealing flap 14 to achieve a compressible and soft, yet supportive inner support structure, and it is this curved, cantilever style support portion 12 that causes the issue just described.